1. Field of the Invention
This invention relates to methods of and a system for counting holes in a web and for detecting missing holes and, particularly, to methods of and a system for counting holes in successive sections of a moving flexible web and for determining whether each section contains the exact number of holes required.
2. Discussion of the Prior Art
In the manufacture of flexible printed circuits, a laminate is processed through many stations in forming the circuits. The laminate initially includes a plastic substrate having copper clad to one, or both, major surfaces thereof. The laminate is available in rolls of substantial lengths, such as 550 feet, and provides a base for the manufacture of many printed circuits of the same pattern formed in successive circuit sections of the laminate. Also, the laminates are available in different widths.
Each section of the laminate is indexed through a punch press to form a plurality of holes and slots therethrough of different sizes and shapes. For example, depending on the code of the circuit to be made, each circuit section could have as few as seventeen holes or as many as 2700 holes. Many of the holes are extremely small and are usually round while other larger holes may be round, square or oblong. Each hole is required in the ultimate formation of the printed circuit in order for the circuit to perform as designed. Thus, it is critically important that the required holes and slots be formed in each circuit section of the copper-clad laminate when the successive sections are indexed through the punch press.
On occasion, the punches of the punch press become worn or damaged, or the punches may be missing. In any case, such defective or missing punches result in a missing hole, or holes, in each of the successive circuit sections. If the missing holes are not detected, a complete length, or many lengths, of the laminate could be processed through the punch press and through the printed circuit forming facilities. The occurrence of the missing holes would not become apparent until after the actual circuits have been formed and are processed through final testing. Since the holes are through-plated during the manufacturing process, it would be a practical impossibility to drill holes in the completed circuit where missing holes are detected during final testing. Consequently, not only would there be a loss of many rolls of the laminate, there would also be a costly loss in processing time, use of equipment and personnel time.
It is possible that more than the required number of punches could be included accidently in the punch press which would result in too many holes in each section of the laminate. This will also result in the loss of rolls of laminate.
Thus, it becomes apparent that some form of inspection of the laminate is required as the successive sections exit from the punch press.
Due to (1) the rapid rate at which the laminate moves through the punch press, (2) the minuteness of many of the holes, (3) the number of holes, (4) the different sizes and shapes of the holes and (5) the length of laminate to be examined, it is a practical impossibility to perform a visual inspection. Thus, it becomes obvious quickly that an automatic hole-detecting system must be used.
Since light can be passed through the holes and slots, it would appear that a light-sensing system operating at a rate compatible with the speed of the moving laminate would be able to count the holes. Further comparison techniques could be employed to determine whether any of the successive sections contain less than the desired number of holes.
In consideration of a light-sensing system, many side-to-side scans of the moving laminate must be employed to insure that the smallest hole is detected and counted. Due to the minuteness of the small holes, the scan frequency of any light-sensing system used must be sufficient to provide at least one scan line to sense the light passing therethrough. Consequently, the larger holes will be scanned several times. Since the light-sensing system would typically respond and count each time light is sensed, each of the larger holes would provide a light-sensed condition each time it is scanned and thereby provide multiple counts for a single hole. Obviously, a system of this type would not satisfy the requirements of examining a laminate having holes of different sizes and shapes.
The pattern of holes and slots is repeated many times along a roll or length of the laminate. If a light-sensing system is used, it must be reset at extremely short intervals to insure that it examines each circuit section with no carryover of hole count from preceding sections.
An examination of commercially available equipment quickly revealed that the available light-sensing systems were not capable of solving the problems outlined above.
Several prior art systems, as outlined below, use a photosensitive device, such as a vidicon or television camera, to scan an image in search of various information such as defects.
U.S. Pat. No. 3,019,347, to J. F. Laycak, teaches the use of a vidicon tube to scan a moving steel slab in search for defects of a light-reflective property differing from the normal light-reflective property of the slab. The total area of all defects in the slab is computable. The sensing of opposite edges of the slab generates pulses which would normally denote defects in the slab. A pulse-delay technique permits the complete cancellation of the edge-generated pulses. Also, pulses generated upon the scanning of very narrow defects are cancelled to minimize error in the final area computation.
U.S. Pat. No. 3,244,810, to D. A. Williams, teaches a system using a conventional television camera to scan a stationary object to obtain a variety of data regarding the object. An intercept scanning technique is employed wherein an imaginary line is formed through the object by using delays based on the first intercept of the object and provides a count pulse each time the line is scanned to indicate the continued presence of the object.
U.S. Pat. No. 3,280,692, to J. A. Milnes et al., teaches the use of a conventional television camera to scan a light-reflecting tin strip in search of flaw-like defects on each of left-hand and right-hand sides of the strip. For example, as each defect is scanned on the left-hand side, a pulse is developed. Where pulses occur on successive scans, it is indicative of a single recurring defect. The first absence of such a pulse denotes the end of the defect. The pulses of each scan are then integrated and converted into a square wave which is differentiated to provide a single pulse to represent the defect. If other defects are detected on the same scans, the pulses developed in response thereto are absorbed in the integration of the pulse of the prior detected defect and ultimately are absorbed in the count of the prior defect. Consequently, this system can count only one defect for each of the left-hand and right-hand sides on each scan. These pulses provide a defect count and are used to compute total area of defect in the strip.
U.S. Pat. No. 3,389,789, to G. L. Watson et al., teaches the use of a television camera to scan a moving discrete object in search of flaws. In a first embodiment, an actuator or indicator is set when the first flaw in the object is detected and remains set until the trailing edge of the moving object trips a switch to reset the system. In a second embodiment, each flaw on selected scan lines are counted as a measure of acceptability of the object. Also, facilities are provided for detecting flaw indications on spaced scan lines and utilizing such data as an indication of a single flaw spanning the spaced scan lines.
U.S. Pat. No. 3,835,332, to R. E. Bridges, teaches the use of a light-sensing scanning system to sense defects in a moving web. Signals are generated when defects are sensed and compared with the amplitude of standard signals. The results of the comparison are displayed and sound an alarm.
U.S. Pat. Nos. 3,188,478; 3,665,444; 3,717,751 and 4,024,381 all teach the use of detection systems to sense holes, objects or defects.
Thus, even though the foregoing patents teach light-sensing systems, none of these patents teach a system for providing a "one" count for each of a plurality of multiple-scanned, light-sensed holes detected on each scan. Nor do they teach a system for providing a "one" count for each of a plurality of multiple-scanned, light-sensed holes of successive sections of a web, comparing a totalization of such "one" counts for each of the successive sections with a preset total and resetting the system after each section is counted in preparation for the counting of the next section of the web.